Split refrigeration system including charge measuring means



1964 E. c. KENNEDY 3,163,016

SPLIT REFRIGERATION SYSTEM INCLUDING CHARGE MEASURING MEANS Filed May 29, 1963 INVENTOR K K I K (I ,1 I 1 S I C.

\-\\'s TORNEY United States Patent Cfifice 3,163,016 Patented Dec. 2Q, 1964 3,163,016 SPLIT REFRIGERATKON SYSTEM BJCLUBEQG CHARGE MEASURING MEANS Edwin C. Kennedy, Tyler, Tex., assignor to General Electric Company, a corporation of New York Filed May 22 1963, Ser. No. 284,154 2 Claims. (Cl. 62--129) The present invention relates to refrigeration systems of the split system type comprising indoor and outdoor units connected by refrigerant lines and is more particularly concerned with systems of this type including means for accurately determining the charge contained in the refrigerant circuit regardless of the lengths of the connecting lines.

The lengths of tubing required to connect the separate units of a split-unit type system vary a great deal depending upon the installation requirements. Thus the total volume of the systems cannot be known until it is finally installed, making it necessary to finalize the refrigerant charge of the particular system after installation.

One means for determining the proper charge of refrigerant in a refrigeration system is broadly disclosed and claimed in the application of Herbert M. Brody,

Serial No. 284,155, now abandoned, filed concurrently herewith and assigned to the same assignee as the present application.

In accordance with the teachings of the Brody application, a refrigeration system including a compressor, a first heat exchanger adapted to be operated as a condenser, a second heat exchanger adapted to operate as an evaporator, and flow control means between the two heat exchangers for normal control of the refrigerant flow, is provided with means for determining or measuring the refrigerant charge which includes means for abnormally or substantially restricting the flow of refrigerant from the condenser so that operation of the compressor will cause substantially all of the refrigerant charge to collect as a liquid and as high pressure gas in the high side volume where the total quantity thereof can be accurately determined. As the invention of the Brody application was made by said Brody prior to my invention, 1, therefore, do not herein claim as my invention anything shown or described in that application, which is to be regarded as prior art with respect to the present application. Rather, my invention is directed specifically to measuring the refrigerant charge in a system of the split type in which the separate units are field connected as required by a pair of refrigerant lines, the lengths of which vary depending upon the particular installation.

The specific features and advantages of the present invention will become apparent as the following description proceeds and the features of novelty which characterize the invention will be pointed out with particularity in the claims annexed to and forming a part of this specification.

In accordance with one aspect of the present invention, there is provided a refrigeration system comprising a first unit and a second unit adapted to be field connected by a pair of refrigerant lines to provide a closed refrigerant circuit. The first unit comprises a circuit component including a heat exchanger connected in series with a refrigerant flow control means which is operable to restrict the flow of refrigerant when the flow of refrigerant is in a direction from the flow control means to the heat eX- changer. The second unit includes a circuit component including a heat exchanger, a refrigerant flow control means and charge determining means connected in series, the flow control means being operable to restrict the flow of refrigerant when the refrigerant flow is in a direction from the flow control means to the heat exchanger. The system also includes a compressor for effecting fiow of refrigerant through the circuit. In the field installation of the units, the flow control means of the first unit is connected by one of the refrigerant lines to the charge determining means of the second unit, the length of this line depending upon the locations of the two units. The charge determining means comprises means for substantially restricting the flow of refrigerant between the units when it is desired to check the charge. For normal operation, this restricting means is bypassed or rendered inoperable. When rendered operable with said compressor operating to discharge refrigerant to the first unit, substan tially all of the refrigerant charge in the system collects as a liquid and a high pressure gas in the refrigerant line connecting the units and in the circuit component of the first unit. When the high side volume is properly sized in proportion to the total refrigerant charge, the proportion of refrigerant Weight distributed between the liquid and the gas phase varies with ambient temperature but due to corresponding change in densities, the level ofthe liquid surface will remain substantially unchanged over a wide range of ambient temperatures. The first unit also includes liquid level indicating means spaced from the connection thereof to said refrigerant lines a distance such that the volume of the portion of the first unit circuit component between the level indicating means and the connection thereof to the refrigerant line is substantially equal to or indicative of the preferred or optimum charge of refrigerant for the system exclusive of the.

volume of the refrigerant line. One or both units may also include charge modifying or storage means. Such means may comprise a dead-end receptacle in heat exchange relationship with a conduit connecting the reversing valve to the unit heat exchanger and having a two way flow connection to a point in the circuit between that heat exchanger and the flow control means of that unit. When the first unit includes such a receptacle the connection also includes a valve for closing the connection during the charge determining cycle.

For a better understanding of the invention reference is made to the following description taken in connection with the accompanying drawing in which the single figure represents diagrammatically a refrigeration system embodying the present invention.

While the invention is applicable to any split refrigeration system, it will be particularly described with reference to a split reversible cycle system or heat pump.

Referring now to the drawing, there is shown a heat pump or reversible refrigeration system which comprises an outdoor unit 1 and an indoor unit 2 which are adapted to be connected in the field during installation of the heat pump by refrigerant lines 3 and 4 to form a closed refrigerant circuit. The lengths of lines 3 and 4 will obviously depend upon the distance between the two units.

The outdoor unit 1 includes a circuit component comprising a conduit 5 and an outdoor heat exchanger 6 connected in series connection with flow control means including a capillary 7 or equivalent pressure reducing means and a bypass line including a check valve 8 which bypasses refri erant around the capillary 7 when the heat pump is operated as a cooling unit and the outdoor heat exchanger 6 is functioning as a condenser. The indoor unit 2 comprises a conduit It an indoor heat exchanger ll, flow control 'means including a capillary 12 and a by pass line including a check valve 14, and charge determining fiow restriction means generally indicated by the numeral 15. The conduit til, heat exchanger 11, flow control means and charge determining means 15 are series connected to form a circuit component in the indoor unit 2. The check valve 14 renders the capillary 12 inoperative or bypasses the capillary 12 when the flow of refrigerant is from the indoor heat exchanger in the direction of the flow control means including the capillary 12.

A compressor 16 having a discharge line 17 and a suction line 18 connected respectively with a reversing valve 19 provides means for effecting flow of refrigerant through the refrigerant circuit including the two units in either direction whereby the indoor unit 2 may be operated either as a heating unit in which the indoor heat exchanger ll. functions as a condenser or as a cooling unit in which the indoor heat exchanger 11 functions as an evaporator. The compressor and reversing valve may be supplied as a separate unit or may be part of either one of the units 1 and 2. In the illustrated embodiment of the invention, the compressor 1d and reversing valve 19 form part of the outdoor unit 1 in which case the reversing valve is connected to the conduit 5 of the unit 1 and to the conduit it) of the indoor unit 2 through the refrigerant line 4.

When the heat pump is operated on the cooling cycle, warm compressed refrigerant from the compressor 16 is directed by the reversing valve 19 through the conduit 5 to the outdoor heat exchanger 6 in which the refrigerant is cooled and condensed. Liquid refrigerant flows from the outdoor heat exchanger 6 through the bypass line including the check valve 8 and the refrigerant line 3, through the normally open valve 22 forming part of the charge determining means 15, the flow control capillary 12 and into the indoor heat exchanger 11 which functions as an evaporator. In the heat exchanger 11 the refrigerant is evaporated by absorbing heat from an air stream circulated over this heat exchanger and the vaporized refrigerant is withdrawn through the conduit 1t) and the connecting refrigerant line 4 by the compressor 16 When the heat pump is operated on the heating cycle, the compressed refrigerant from the compressor is directed by the reversing valve 19 in a reverse direction so that the warm compressed refrigerant passes through the refrigerant line 41 and the conduit it) into the indoor heat exchanger 11 which then functions as a condenser. In the indoor heat exchanger 11, the refrigerant condenses and gives up heat to the air stream circulated over this heat exchanger. The liquified refrigerant bypasses the capillary 12 through the check valve 14 and, flows through the normally open valve 22 and the line 3 to the capillary 7. From the capillary 7 the refrigerant expands into the outdoor coil 6 where at a reduced pressure, it is evaporated. The vaporized refrigerant is withdrawn by the compressor through the conduit 5.

' While the capillaries 7 and 12 are designed to provide different flow rates of refrigerant on the heating and cooling cycles, it is also desirable in many heat pump systems including fixed or capillary tube flow control means to modify or change the circulating refrigerant charge in order to obtain the most eflicient operation of the system under a range of operating conditions. In the illustrated embodiment of the invention, this is accomplished by means of dead-end or two way flow storage receptacles associated respectively with the units 1 and 2. More specifically, there is provided a dead-end storage receptacle 24 as part of the outdoor unit 1 and a similar dead-end storage receptacle 25 forming part of the indoor unit 2. The receptacle 24 is connected by means of a two way flow line 26 to a portion of the circuit component of the outdoor unit 1 which operates at the same pressure as the heat exchanger 6, as; for example to that part of the circuit between the outdoor heat exchanger 6 and the capillary 7. The receptacle 25 is similarly connected by means of the connection 28 to a portion of the circuit between the indoor heat exchanger 11 and the capillary 12. For the purpose of effecting automatic withdrawal of refrigerant from the system or automatic discharge of refrigerant into the system by one or both of the receptacles in order to regulate the effective or circulating charge in the system under various conditions of operation, the receptacle 24 is heat exchanged with the conduit 5 while the receptacle 25 is heat exchanged with the conduit 1%, each of which conduits connect their respective units to the reversing valve 19. Thus, when the heat pump is operating on the cooling cycle so that hot compressed refrigerant is being conducted from the compressor 16 through the conduit 5, the receptacle 24 is warmed by this hot refrigerant causing most or all of any liquid refrigerant contained or stored in the receptacle to be discharged into the circuit. During the same cycle of operation the receptacle 25 is cooled by loW pressure refrigerant returning to the compressor through the conduit 10 so that refrigerant will be withdrawn from the system and condensed in the receptacle 25. Conversely, during the heating cycle operation of the heat pump, hot compressed refrigerant flowing to the indoor heat exchanger 11 through the conduit 10 warms the receptacle 25 causing refrigerant stored therein to be discharged into the system while at the same time the receptacle 24 tends to be cooled by low pressure refrigerant returning to the compressor through the conduit 5 so that refrigerant tends to condense and collect in the receptacle 24 The withdrawal from or the addition to the circuit of refrigerant by the modulator receptacles 2d and 25 is influenced not only by the heat exchange thereof with certain portions of the circuit but also by the particular system pressure and temperature conditions in those portions of the systems to which these receptacles are respectively connected by connections 26 and 23.

In the field installation of a heat pump of the split'unit type, the indoor unit 2 is generally placed within the enclosure while the outdoor unit 1 is installed outside of the enclosure, sometimes some distance away. Hence the lengths of the refrigerant lines 3 and 4 required to connect the separate units will vary a great deal from installation to installation so that the total volume of the system and hence the optimum refrigerant charge for the system will depend upon the lengths of these lines. The length of the line 3 is most critical because of the fact that this line, which connects the two flow control means including the capillaries 7 and 12, is part of the high pressure side of the system regardless of whether the heat pump is operating on the heating cycle or on the cooling cycle so that it is normally filled with liquid refrigerant on both cycles. It is therefore very desirable that the volume of this line be included in any measure of the optimum refrigerant charge for the system.

After the two units have been connected by the lines 3 and 4, the system may be charged through a suitable charging valve (not shown) with a charge calculated to be approximately correct for the system. In some cases, the units 1 and 2 may be precharged with what is calculated to be the optimum charge for the average installation. In either case, after complete assembly of the heat pump in the field, a final check of the charge is desirable to be sure that the system contains the optimum amount of refrigerant.

As taught in the aforementioned Brody application, the refrigerant charge in a system can be quickly and accurately measured by abnormally restricting the flow of refrigerant from the condenser component so that all of the charge will collect ahead of the restriction for measure- Inent thereof. By providing liquid level indicating means ahead of the restriction and spaced therefrom a distance such that the volume of the circuit between the indicating and restricting means is equal to the optimum charge, when a liquidgas interface is present at the indicating means, the Serviceman knows that the system is properly charged.

This method requires a predetermined positioning of the level indicating and restricting means based on a knowledge of the final volume of the total system.

The total volume of a split heat pump system including connecting lines such as lines 3 and 4- cannot be known until after the system is installed. In accordance with the present invention an accurate check of the charge regardless of the lengths of lines 3 and 4 is obtained by so positioning the flow restricting means and the level indicating means in the system that the liquid contained in the line 3 will be automatically compensated for during the charge determining operation. More specifically, the flow restricting means is so positioned in the indoor unit that it is connected directly to one end of the line 3 and the level indicating means 29, such as a sight glass, is incorporated at the proper point in the outdoor unit 1. In the illustrated embodiment of the invention, the flow determining means 15 forms part of the indoor unit 2 immediately adjacent the connection of the indoor unit 2 to the refrigerant line 3 while the indicating means is in one pass of the heat exchanger 6.

The flow restricting means 15 comprises the normally opened valve 22 including a port 30 which is open during operation of the heat pump on both the heating and the cooling cycles. A capillary flow restricting means 31 bypassing the valve 22 or more specifically the port 30, provides means for introducing an abnormal or substantial restriction between the high and low pressure sides of the system, that is, between the indoor and outdoor units 1 and 2 when the valve 22 closes the port 3h.

The charge measuring operation or cycle comprises operating the unit in such a manner that with the compressor 16 operating and the flow restriction 31 introduced into the circuit, substantially all of the refrigerant charge will be transferred to a portion of the system including the connecting refrigerant line 3 where it can be measured. Thus for the illustrated system, the reversing valve 19 is positioned so that the outdoor unit 1 operates as a high pressure unit and refrigerant condenser and collects in the portion of the circuit ahead of or upstream from the valve 22. Thus the refrigerant charge is collected in the portion of the circuit including line 3 and the outdoor unit refrigerant component ahead of the restriction 31. The serviceman can determine whether or not the charge is proper by observing the refrigerant condition at the liquid level indicating means 29. This indicating means is spaced a distance from the end 35 of the unit 1 connected to the refrigerant line 3 such that the volume of the refrigerant circuit between the level indicating means 29 and the end 35 of the outdoor unit which is connected to line 3 has the same volume as the optimum charge of refrigerant for the circuit exclusive of the line 3. Since the line 3 contains liquid refrigerant on either of the normal cycles of operation of the heat pump, and since the small amount of gaseous refrigerant present in the line 4 can be disre garded, this volume of the circuit component in the outdoor unit 1 is an accurate measurement of the proper charge for the heat pump regardless of the lengths of the lines 3 and 4.

As has been previously indicated, the charge in the system is determined by observing the conditions at the level indicating means or sight glass 29. If there is a liquid level, that is, a liquid-gas interface showing at the sight glass, the charge is correct. If a refrigerant flow of gas or gas and liquid is observed in the sight glass, the charge is low and additional refrigerant should be added to the system through a charging valve until a liquid level is observed. If the sight glass shows only liquid refrigerant, the charge is excessive and some refrigerant should be bled off through a suitable bleed off valve until a liquidgas level or interface is observed in the sight glass.

For proper operation during the charge determining cycle, it is necessary to assure that all of the liquid refrigerant contained in the refrigerant circuit will be transferred to that portion of the system between the liquid level indicator 29 and the restrictor 31 so that the total system charge can be accurately measured. Thus, if there are any areas of the system in which liquid refrigerant may become trapped during the charge measuring cycle or in which liquid refrigerant may collect during this cycle, it is necessary to assure transfer of this liquid to the high side of the system. By providing a minimum flow through the capillary restrictor 31 during the charge determined cycle, any liquid which might tend to become trapped in the main refrigerant circuit will be swept through the system into the heat exchanger 6.

As is pointed out more fully in the aforementioned Brody application, the sizing or flow rate of the restriction 31 is not particularly critical provided the refrigerant flow through the system during the charge measuring cycle is substantially less than that obtained under ordinary conditions of normal operation. In other words, the restrictor flow rate should be such that the compressor will operate at a relatively low suction pressure and will pump the evaporator or low pressure side of the system dry of all liquid.

When the system includes'charge modulating means such as the receptacles 24 and 25, it is necessary to be sure that no liquid refrigerant is contained in the receptacles during the charge measuring period or in other words that all of it be transferred to the measuring portion of the circuit. Since the receptacle 25 is operating at abnormally low suction pressure during the charge measuring cycle, any refrigerant contained therein will be evaporated during the early part of the operation of the system on the charge measuring cycle. However, since the receptacle Z4 is connected to the high pressure portion of the system ahead of the flow restriction 31, means should be provided for removing all liquid refrigerant from this receptacle for charge measuring purposes. To this end there can be employed a valve 3'7 in the conduit 26 which is adapted to be closed during the charge measuring cycle. Before this valve is closed, the receptacle 24 is emptied of liquid refrigerant by operating the system on the cooling cycle for a short period of time until this receptacle is warmed and completely emptied by action of the warm compressed refrigerant flowing through the conduit 5. Alternatively, this can be done by operating the system on what would normally be considered the heating cycle of operation but with the valve 22 closing the port St in which case the lower than normal pressure obtained in the refrigerant circuit components of the outdoor unit ll will cause any liquid refrigerant in the receptacle 24 to evaporate and to be transferred to the refrigerant components of the indoor unit 2. In either case, after the receptacle 24 has been completely emptied, valve 37 is closed so that during the charge measuring cycle only those portions of the outdoor unit 1 forming part of the refrigerant flow circuit between the level indicating means 29 and the outlet 35 can receive and store liquid refrigerant.

While the invention has been described with specific reference to a system including fixed flow control means such as a capillary tube for controlling the flow of refrigerant during normal operating cycles it will be obvious that it is also applicable to various split systems including expansion valves instead of fixed flow control means. Other modifications of the invention will also occur to those skilled in the art and it is to be understood, therefore, that the invention is not limited to the particular embodiment disclosed and that it is intended to cover by the appended claims all modifications which are within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

l. A reversible refrigeration system comprising a first unit and a second unit adapted for field connection to a pair of refrigerant lines of lengths determined by the installation to provide a closed refrigerant circuit;

said first unit including a circuit component comprising a conduit, a heat exchanger and a refrigerant flow control means connected in series, and a charge modifying means comprising a dead-end receptacle in heat exchange relationship with said conduit and having a two-Way flow connection to said component between said heat exchanger and said flow control means, said flow control means being operable to restrict the flow of refrigerant when the flow of refrigerant is in a direction from said flow control means to said heat exchanger;

said second unit including a circuit component includagreaor e 7. ing a heat exchanger, refrigerant flow control means and charge determining means connected in series, said fibw control means operable to restrict the flow of refrigerant when the refrigerant flow is in a direction from said flow control means to said heat exchanger;

means including a compressor and reversing valve means for reversibly connecting said compressor to said heat exchangers for elfecting flow of refrigerant through said circuit in either direction whereby said reversible refrigerating system may be operated on a cooling cycle in which one unit functions as a heating unit or on a heating cycle in which said one unit functions as a cooling unit;

said flow control means of said first unit being connected by one of said refrigerant lines to said charge determining means;

said charge determining means comprising flow restricting means and means for rendering said flow restricting means operable to restrict the flow of refrigerant from said first unit component to said second unit component so that with said compressor operating to discharge refrigerant to said first unit heat exchanger substantially all of the refrigerant charge in said systern will collect as a liquid in said one refrigerant line and in said first unit heat exchanger;

said first unit component including liquid level indicating means spaced from the connection thereof to said one refrigerant line a distance such that the volume of the portion of said first unit component between said indicating means and said connection is a measure of the preferred charge of liquid refrigerant for the system exclusive of said refrigerant lines, said two-Way flow connection including a normally openvalve adapted to be closed during the time the charge in said system is being measured to prevent liquid refrigerant from entering said first unit receptacle.

2. A reversible refrigeration system comprising a first unit and a second unit adapted for field connection to a pair of refrigerant lines of lengths determined by the installation to provide a closed refrigerant circuit;

said first unit including a circuit component comprising a conduit, a heat exchanger and a refrigerant flow control means connected in series, and a charge modifying means comprising a dead-end receptacle in heat exchange relationship with said conduit and having a two way flow connection to said component between said heat exchanger and said flow control means, said flow control means being operable to restrict the flow of refrigerant when the flow of refrigerant is in a direction from said flow control means to said heat exchanger;

said second unit including a circuit component including a conduit, a heat exchanger, a refrigerant flow control means and charge determining means connected in series, and a charge modifying means including a dead-end storage receptacle in heat exchange relationship with said conduit and having a two way flow connection to said unit between said heat exchanger and said flow control means, said flow control means being operable to restrict the flow of refrigerant when the refrigerant flow is in a direction from said flow control means to said heat exchanger;

means including a compressor and reversing valve means for reversibly connecting said compressor to said conduits for effecting flow of refrigerant through said circuit in either direction whereby said reversible refrigerating system may be operated on a cooling cycle in which one unit functions as a heating unit or on a heating cycle in which said one unit functions as a cooling unit;

said flow control means of said first unit being connected by one of said refrigerant lines to said charge determining means;

said charge determining means comprising flow restricting means and means for rendering said flow restricting means operable to restrict the flow of refrigerant from said first unit component to said second unit component so that with said compressor operating to discharge refrigerant to said first unit heat exchanger substantially all of the refrigerant charge in said systern will collect as a liquid in said one refrigerant line and in said first unit heat exchanger;

said first unit component including liquid level indicating means spaced from the connection thereof to said one refrigerant line a distance such that the volume of the portion of said first unit circuit component between said indicating means and said connection is a measure of the preferred charge of liquid refrigerant for the system exclusive of the volume of said one of said refrigerant lines;

said first unit two Way flow connection including a normally open valve adapted to be closed during the time the charge in said system is being measured to prevent liquid refrigerant from entering said first unit receptacle.

References Cited by the Examiner UNITED STATES PATENTS 1,533,336 4/25 Pownall 62-292 l,8 1 5,962 7/ 3 1 Andrews 62'-149 2,759,340 8/ 56 Besl'in- 62-292 3,006,155 10/61 Vanderlee et al 62-149 ROBERT A. OLEARY, Primary Examiner. 

1. A REVERSIBLE REFRIGERATION SYSTEM COMPRISING A FIRST UNIT AND A SECOND UNIT ADAPTED FOR FIELD CONNECTION TO A PAIR OF REFRIGERANT LINES OF LENGTHS DETERMINED BY THE INSTALLATION TO PROVIDE A CLOSED REFRIGERANT CIRCUIT; SAID FIRST UNIT INCLUDING A CIRCUIT COMPONENT COMPRISING A CONDUIT, A HEAT EXCHANGER AND A REFRIGERANT FLOW CONTROL MEANS CONNECTED IN SERIES, AND A CHARGE MODIFYING MEANS COMPRISING A DEAD-END RECEPTACLE IN HEAT EXCHANGE RELATIONSHIP WITH SAID CONDUIT AND HAVING A TWO-WAY FLOW CONNECTION TO SAID COMPONENT BETWEEN SAID HEAT EXCHANGER AND SAID FLOW CONTROL MEANS, SAID FLOW CONTROL MEANS BEING OPERABLE TO RESTRICT THE FLOW OF REFRIGERANT WHEN THE FLOW OF REFRIGERANT IS IN A DIRECTION FROM SAID FLOW CONTROL MEANS TO SAID HEAT EXCHANGER; SAID SECOND UNIT INCLUDING A CIRCUIT COMPONENT INCLUDING A HEAT EXCHANGER, REFRIGERANT FLOW CONTROL MEANS AND CHARGE DETERMINING MEANS CONNECTED IN SERIES SAID FLOW CONTROL MEANS OPERABLE TO RESTRICT THE FLOW OF REFRIGERANT WHEN THE REFRIGERANT FLOW IS IN A DIRECTION FROM SAID FLOW CONTROL MEANS TO SAID HEAT EXCHANGER; MEANS INCLUDING A COMPRESSOR AND REVERSING VALVE MEANS FOR REVERSIBLY CONNECTING SAID COMPRESSOR TO SAID HEAT EXCHANGERS FOR EFFECTING FLOW OF REFRIGERANT THROUGH SAID CIRCUIT IN EITHER DIRECTION WHEREBY SAID REVERSIBLE REFRIGERATING SYSTEM MAY BE OPERATED ON A COOLING CYCLE IN WHICH ONE UNIT FUNCTIONS AS A HEATING UNIT OR ON A HEATING CYCLE IN WHICH SAID ONE UNIT FUNCTIONS AS A COOLING UNIT; SAID FLOW CONTROL MEANS OF SAID FIRST UNIT BEING CONNECTED BY ONE OF SAID REFRIGERANT LINES TO SAID CHARGE DETERMINING MEANS; SAID CHARGE DETERMINING MEANS COMPRISING FLOW RESTRICTING MEANS AND MEANS FOR RENDERING SAID FLOW RESTRICTING MEANS OPERABLE TO RESTRICT THE FLOW OR REFRIGERANT FROM SAID FIRST UNIT COMPONENT TO SAID SECOND UNIT COMPONENT SO THAT WITH SAID COMPRESSOR OPERATING TO DISCHARGE REFRIGERANT TO SAID FIRST UNIT HEAT EXCHANGER SUBSTANTIALLY ALL OF THE REFRIGERANT CHARGE IN SAID SYSTEM WILL COLLECT AS A LIQUID IN SAID ONE REFRIGERANT LINE AND IN SAID FIRST UNIT HEAT EXCHANGER; SAID FIRST UNIT COMPONENT INCLUDING LIQUID LEVEL INDICATING MEANS SPACED FROM THE CONNECTION THEREOF TO SAID ONE REFRIGERANT LINE A DISTANCE SUCH THAT THE VOLUME OF THE PORTION OF SAID FIRST UNIT COMPONENT BETWEEN SAID INDICATING MEANS AND SAID CONNECTION IN A MEASURE OF THE PREFERRED CHARGE OF LIQUID REFRIGERANT FOR THE SYSTEM EXCLUSIVE OF SAID REFRIGERANT LINES, SAID TWO-WAY FLOW CONNECTION INCLUDING A NORMALLY OPEN VALVE ADAPTED TO BE CLOSED DURING THE TIME THE CHARGE IN SAID SYSTEM IS BEING MEASURED TO PREVENT LIQUID REFRIGERANT FROM ENTERING SAID FIRST UNIT RECEPTACLE. 